Oscillation-type compressor

ABSTRACT

A tightly closed casing has an inside space for storing coolant gas. A block is accommodated in this casing. A motor includes a stator and a mover. A piston is connected to the mover of the motor. A movable element includes the mover of the motor and the piston. A stationary element includes the stator of the motor and the block. An elastic element has a portion fixed to the movable element and another portion fixed to the stationary element. A cylinder is shiftable in an axial direction with respect the block. A shifting device shifts the cylinder in the axial direction.

This application is a divisional of U.S. patent application Ser. No.09/740,949 filed Dec. 21, 2000 which in turn was a divisional of parentpatent application Ser. No. 09/170,035 filed Oct. 13, 1998 now U.S. Pat.No. 6,203,292.

BACKGROUND OF THE INVENTION

The present invention relates to an oscillation-type compressorpreferably used in a refrigerator and an air-conditioner.

Various conventional oscillation-type compressors are disclosed inPublished Japanese Patent Applications Nos. Kokai 51-57009, Kokai8-247025, Kokai 9-324764, and Kokai 4-347460.

The oscillation-type compressors basically comprise a movable elementincluding a piston and a stationary element including a cylinder, sothat gas is introduced into a compression chamber defined by the pistonand the cylinder and compressed by the piston that reciprocates in theaxial direction.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an oscillation-typecompressor capable of minimizing the top clearance of the piston in agiven piton stroke and maintaining efficient compressor operations.

Another object of the present invention is to realize a practicalcooling device, such as a refrigerator, which is capable ofautomatically increasing the stroke of the piston in response to a highambient air temperature so that the cooling power can be sufficientlyobtained even in such a high load condition and. is also capable ofautomatically reducing the stroke of the piston in response to adecreased ambient air temperature, thereby realizing efficientcompressor operation in accordance with the driving conditions of thecooling device without using additional detecting and control devices.

Another object of the present invention is to provide anoscillation-type compressor capable of suppressing the top clearance ofthe piston even in the start-up operation where the piston is operatedwith short strokes, thereby realizing efficient compressor operation.

Another object of the present invention is to provide anoscillation-type compressor capable of stabilizing the cylinder positionduring an ordinary operation.

Another object of the present invention is to provide anoscillation-type compressor capable of optimizing the piston positionwith respect to the cylinder position irrespective of changed operatingpressure conditions, thereby minimizing the top clearance and realizingefficient compressor operation.

Another object of the present invention is to provide anoscillation-type compressor capable of preventing the piston fromcolliding with the exhaust valve when the piston stroke is increased,thereby eliminating any damage and noise.

Another object of the present invention is to provide anoscillation-type compressor having an exhaust or intake pipe shiftablein the axial direction even when large vibration occurs in the axialdirection, thereby reducing a large amplitude stress repetitively actingon the exhaust or intake pipe.

In order to accomplish the above and other related objects, one aspectof the present invention provides an oscillation-type compressorcomprising a tightly closed casing having an inside space for storingcoolant gas, a block accommodated in the tightly closed casing, a motorincluding a stator and a mover, a piston connected to the mover of themotor, a movable element including the mover of the motor and thepiston, a stationary element including the stator of the motor and theblock, an elastic element having a portion fixed to the movable elementand another portion fixed to the stationary element, a cylindershiftable in an axial direction with respect the block, and a shiftingdevice for shifting the cylinder in the axial direction.

Another aspect of the present invention provides an oscillation-typecompressor comprising a tightly closed casing having an inside space forstoring coolant gas, a block accommodated in the tightly closed casing,a motor including a stator and a mover, a piston connected to the moverof the motor, a movable element including the mover of the motor and thepiston, a stationary element including the stator of the motor and theblock, an elastic element having one portion fixed to the movableelement and another portion fixed to the stationary element, a cylindershiftable with respect the block, a cylinder head fixed to the cylinder,back-pressure chambers formed in the coolant gas space and airtightlypartitioned by an integral unit including at least one of the cylinderand the cylinder head, and at least one of the back-pressure chambersbeing held at a low pressure level and another one of the back-pressurechambers being held at a high pressure level.

It is preferable that this oscillation-type compressor further comprisesan elastic member having one end connected to the integral unitincluding at least one of the cylinder and the cylinder head and theother end connected to the stationary element, and further comprises acylinder position detecting sensor fixed to one of the stationaryelement and the cylinder.

Another aspect of the present invention provides an oscillation-typecompressor, comprising a tightly closed casing having an inside spacefor storing coolant gas, a block accommodated in the tightly closedcasing, a motor including a stator and a mover, a piston connected tothe mover of the motor, a movable element including the mover of themotor and the piston, a stationary element including the stator of themotor and the block, an elastic element having one portion fixed to themovable element and another portion fixed to the stationary element, acylinder fixed to the block or shiftable in an axial direction withrespect the block, a cylinder head fixed to the cylinder, an auxiliarypipe having one end shiftable in the axial direction with respect to oneof an exhaust pipe and an intake pipe and the other end fixed to one ofthe cylinder and the cylinder head.

Furthermore, another object of the present invention is to provided anoscillation-type compressor capable of causing the cylinder to shifttoward the top dead center when the ambient temperature is high andtherefore the required cooling power is high.

Another object of the present invention is to provide anoscillation-type compressor capable of surely reducing the pulsation ofthe compressor even when the discharged gas amount increases in responseto an increased stroke, thereby suppressing noise and vibration.

Another object of the present invention is to provide anoscillation-type compressor capable of preventing the compressorefficiency from deteriorating due to the leakage of coolant gas.

Another object of the present invention is to provide anoscillation-type compressor capable of preventing the cylinder fromshifting excessively toward the top dead center, while causing noproblems in the reliability of the elastic element or the like.

In order to accomplish the above and other related objects, one aspectof the present invention provides an oscillation-type compressorcomprising a block and a piston accommodated in a tightly closed casing,a motor including a stator and a mover, a movable element including themover and the piston, a stationary element including the block and thestator, an elastic element having a portion fixed to the movable elementand another portion fixed to the stationary element, a cylinderaccommodating the piston so that the piston is shiftable in an axialdirection, the cylinder being inserted in the block so as to reciprocatein the axial direction with a closed space formed between the block andthe cylinder, a cylinder head comprising an exhaust chamber and attachedto the cylinder, and a communication passage connecting the closed spaceand the exhaust chamber.

It is preferable that the above-described closed space is connected toan outside space via an exhaust pipe. And, a slide surface between thecylinder and the block is connected to a lower part of the closed spacevia a passage. A groove is provided on a slide surface of one of thecylinder and the block.

Furthermore, another object to the present invention is to provide anoscillation-type compressor capable of increasing the top clearance ofthe piston in response to a decreased ambient air temperature or adecreased load without deteriorating the operating efficiency of thecompressor.

Another object of the present invention is to provide anoscillation-type compressor capable of causing the stator of the motorto shift in a direction opposed to the compression chamber when the topdead center position of the piston is dislocated toward the cylinderhead, thereby preventing the piston from colliding with the exhaustvalve.

Another object of the present invention is to provide anoscillation-type compressor capable of shifting the motor stator in thedirection opposed to the compression chamber when the compressor isstopped.

In order to accomplish the above and other related objects, one aspectof the present invention provides an oscillation-type compressorcomprising a tightly closed casing having an inside space for storingcoolant gas, a cylinder accommodated in the tightly closed casing, amotor including a stator and a mover, a piston connected to the mover ofthe motor, a movable element including the mover of the motor and thepiston, a stationary element including the stator of the motor and thecylinder, an elastic element having a portion fixed to the movableelement and another portion fixed to the stationary element, a pitonposition detecting sensor detecting the position of the piston, top deadcenter position calculating means for calculating a top dead centerposition of the piston based on a piston position signal obtained fromthe piton position detecting sensor, amplitude control means forcontrolling an amplitude of the mover in accordance with a differencebetween the top dead center position and a selected top dead centerreference value, and top dead center reference value changing means forchanging the top dead center reference value.

Another aspect of the present invention provides an oscillation-typecompressor comprising a tightly closed casing having an inside space forstoring coolant gas, a cylinder and a block accommodated in the tightlyclosed casing, a motor including a stator and a mover, a pistonconnected to the mover of the motor, a movable element including themover of the motor and the piston, a stationary element including thestator of the motor, the cylinder and the block, an elastic elementhaving a portion fixed to the movable element and another portion fixedto the stationary element, the stator of the motor or a movable statorbase connected to the stator being partly coupled with the stationaryelement so as to reciprocate in an axial direction in response to apressure imbalance between back-pressure chambers formed therebetween,and a pressure control mechanism for controlling the pressures of theback-pressure chambers.

It is preferable that a shifting means is provided for shifting thestator of the motor. in a direction opposed to the compression chamberwhen the compressor is stopped.

Furthermore, another object of the present invention is to reduce theweight of a sensor core attached to the movable element to realize acompact displacement detector, thereby obtaining a higher resonancefrequency and realizing a high power compressor.

Another object of the present invention is to provide a displacementdetector having a limited detection range, thereby improving theaccuracy in the measurement of the piston position in the vicinity ofthe top dead center.

Another object of the present invention is to provide the weight of themovable element, thereby suppressing vibration.

Another object of the present invention is to provide the cooling powerfrom deteriorating due to the coolant gas leakage from the compressionchamber.

Another object of the present invention is to reduce the slide lossbetween the cylinder and the piston, thereby improving the compressorefficiency.

In order to accomplish the above and other related objects, one aspectof the present invention provides an oscillation-type compressorcomprising a block and a piston, a motor including a stator and a mover,a movable element including the mover and the piston, a stationaryelement including the block and the stator, an elastic element having aportion fixed to the movable element and another portion fixed to thestationary element, a cylinder accommodating the piston so as to allowthe piston reciprocating in an axial direction, a displacement detectorconnected to the piston in the axial direction for detecting a positionnear a top dead center of the piston, top dead center position detectingmeans for obtaining the top dead center position of the piston based ona signal obtained from the displacement detector, current/voltagedetecting means for detecting a current or voltage value of the motor,and power supply means for changing the voltage applied to the motorbased on output signals of the top dead center position detecting meansand the current/voltage detecting means.

Another aspect of the present invention provides an oscillation-typecompressor comprising a block and a piston, a motor including a statorand a mover, a movable element including the mover and the piston, astationary element including the block and the stator, an elasticelement having a portion fixed to the movable element and anotherportion fixed to the stationary element, a cylinder accommodating thepiston so as to allow the piston reciprocating in an axial direction,and a displacement detector attached to the movable element and thestationary element at a radially inward portion with respect to thestator of the motor.

Another aspect of the present invention provides an oscillation-typecompressor comprising a block and a piston, a motor including a statorand a mover, a movable element including the mover and the piston, astationary element including the block and the stator, an elasticelement having a portion fixed to the movable element and anotherportion fixed to the stationary element, a rotational directionrestricting mechanism for limiting the rotation of the elastic elementabout a piston shaft in a single direction, a cylinder accommodating thepiston so as to allow the piston reciprocating in an axial direction,and a dynamic pressure generating mechanism provided on at least one ofthe piston and the cylinder.

Furthermore, another object of the present invention is to provide anoscillation-type compressor capable of sufficiently supporting themovable element in the radial direction at a portion other than theslide portion between the piston and the cylinder even when the pistonis positioned near the top dead center or the bottom dead center andtherefore the elastic element cannot sufficiently support the movableelement in the radial direction due to reduced rigidity.

Another object of the present invention is to provide anoscillation-type compressor capable of preventing the piston fromcolliding with the cylinder head or the exhaust valve when the movableelement including the piston shifts toward the compression chamber dueto the insufficient pressurization occurring immediately after thestartup of the compressor or when the ambient air temperature is low.

Another object of the present invention is to provide anoscillation-type compressor capable of preventing the movable elementfrom excessively shifting away from the compression chamber in responseto extremely changed operating conditions.

In order to accomplish the above and other related objects, one aspectof the present invention provides an oscillation-type compressorcomprising a tightly closed casing, a piston and a cylinder accommodatedin the tightly closed casing, a motor including a stator and a mover, astationary element including the cylinder and the stator of the motor, amovable element including the piston and the mover of the motor, anelastic element having a portion fixed to the movable element andanother portion fixed to the stationary element, and a support mechanismfor supporting the movable element in a radial direction when the pistonis positioned near a top dead center position or a bottom dead center.

Another aspect of the present invention provides an oscillation-typecompressor comprising a tightly closed casing, a piston and a cylinderaccommodated in the tightly closed casing, a motor including a statorand a mover, a stationary element including the cylinder and the statorof the motor, a movable element including the piston and the mover ofthe motor, an elastic element having a portion fixed to the movableelement and another portion fixed to the stationary element, and aposition changing mechanism associated with the movable element forchanging an axial position of the movable element.

It is preferable that this oscillation-type compressor further comprisesa stopper for limiting an axial shift amount of the movable elementchanged by the position changing mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription which is to be read in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a first embodiment of the presentinvention;

FIG. 2 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a second embodiment of the presentinvention;

FIG. 3 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a third embodiment of the presentinvention;

FIG. 4 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a fourth embodiment of the presentinvention;

FIG. 5 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a fifth embodiment of the presentinvention;

FIG. 6 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a sixth embodiment of the presentinvention;

FIG. 7 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a seventh embodiment of the presentinvention;

FIG. 8 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with an eighth embodiment of the presentinvention;

FIG. 9 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a ninth embodiment of the presentinvention;

FIG. 10 is a vertical cross-sectional view showing an operated conditionof the oscillation-type compressor in accordance with the ninthembodiment of the present invention;

FIG. 11 is a vertical cross-sectional view showing an arrangement of anoscillation-type compressor in accordance with a tenth embodiment of thepresent invention;

FIG. 12 is a graph showing characteristics of the oscillation-typecompressor in accordance with the tenth embodiment of the presentinvention;

FIG. 13 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with an eleventh embodiment of the presentinvention;

FIG. 14 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a twelfth embodiment of the presentinvention;

FIG. 15 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a thirteenth embodiment of the presentinvention;

FIG. 16 is a diagram showing an electric circuit of the oscillation-typecompressor in accordance with the thirteenth embodiment of the presentinvention;

FIG. 17 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a fourteenth embodiment of the presentinvention;

FIG. 18 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a fifteenth embodiment of the presentinvention;

FIG. 19 is a plan view showing an elastic element used in theoscillation-type compressor in accordance with the fifteenth embodimentof the present invention.

FIG. 20 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a sixteenth embodiment of the presentinvention;

FIG. 21 is a view showing an elastic member used in the oscillation-typecompressor in accordance with the sixteenth embodiment of the presentinvention;

FIG. 22 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a seventeenth embodiment of the presentinvention; and

FIG. 23 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with an eighteenth embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be explained in moredetail with reference to the attached drawings. Identical parts aredenoted by the same reference numerals throughout the drawings.

First Embodiment

FIG. 1 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a first embodiment of the presentinvention.

The oscillation-type compressor comprises a tightly closed casing 1having an inside space 1 a for storing coolant gas and a main body 2. Amotor 3 includes a stator 3 a and a mover 3 b. The mover 3 b is fixed toa piton 5. The main body 2 is roughly constituted by a movable element12 and a stationary element 13. The movable element 12 includes themover 3 b of the motor 3 and the piston 5. The stationary element 13includes a cylinder 4, the stator 3 a of the motor 3 and a block 6. Themain body 2 is elastically supported by a suspension spring (not shown)in the tightly closed casing 1. Lubrication oil 11 is stored in thelower portion of the tightly closed casing 1.

An elastic element 8 comprises a plurality of elastic members 8 astacked or multilayered in an axial direction and spaced via interveningradially outer spacers 8 d and an radially inner spacers 8 e. An innercylindrical edge 8 b of each elastic element 8 is fixed to the piston 5.An outer cylindrical edge 8 c of the elastic element 8 is fixed to theblock 6.

The cylinder 4 and the elastic element 8 cooperatively support thepiston 5 so as to be slidable and reciprocate in the axial direction.The cylinder 4 and the piston 5 cooperatively define a compressionchamber 9.

Next, compression mechanism of the above-described oscillation-typecompressor will be explained. First, alternating current of an AC powersource is half-wave rectified and supplied to the stator 3 a. A magneticfield generated by the stator 3 a attracts the mover 3 b fixed to thepiston 5 based on the principle of magnetic variable resistance. Whenthe mover 3 b shifts in the axial direction, the elastic element 8disposed between the mover 3 b and the block 6 resiliently deforms inresponse to the shift movement of the piston 5, storing an elastic forcetherein. When the elastic force stored in the elastic element 8 issufficiently increased, the mover 3 b is pushed back to the originalposition. Continuous repetition of this cycle reciprocates the piston 5in the axial direction.

Coolant gas of a cooling system (not shown) is introduced into alow-pressure chamber 7 a of a cylinder head 7, and then enters thecompression chamber 9 of the cylinder 4 via an intake valve (not shown)disposed in the cylinder head 7. The coolant gas introduced in thecompression chamber 9 is compressed by the piston 5 which reciprocatesin the above-described manner.

The compressed coolant gas then enters a high-pressure chamber 7 b ofthe cylinder head 7 via an exhaust valve (not shown), and then exits thecylinder head 7 to the cooling system.

According to the first embodiment, the cylinder 4 is integral with thecylinder head 7 and shiftable in the axial direction with respect to theblock 6 when driven by a shifting device 16. The shifting device 16comprises a rack 16 b provided on an axially extending surface of thecylinder 4. A pinion 16 b, rotatably supported to the stationary element13, such as the block 6, meshes with the rack 16 b so as to a constitutea rack-and-pinion mechanism. Thus, the first embodiment provides theshifting device 16 for flexibly shifting the piston 5 in the axialdirection with respect to the block 6.

Operation of the oscillation-type compressor in accordance with thefirst embodiment will be explained hereinafter.

During a compressing operation of the compressor, the cooling power canbe reduced by lowering the voltage applied to the motor 3 so as toreduce the stroke of the piston 5.

In this case, the top clearance of the piston 5 may increase inproportion to reduction of the piston stroke. However, according to thefirst embodiment, the shifting device 16 can shift the cylinder 4 towardthe compression chamber 9 so as to reduce the volume of the compressionchamber 9, thereby canceling the increased top clearance and maintainthe top clearance at a constant value. Thus, re-expansion loss isreduced and efficiency can be maintained adequately.

Furthermore, when an increased cooling power is required, an increasedvoltage is applied to the motor 3 so as to increase the stroke of thepiston 5. In this case, the top clearance decreases due to the increasedstroke of the piston 5. The piston 5 may collide with the cylinder head7. However, according to the first embodiment, the shifting device 16can shift the cylinder 4 away from the compression chamber 9 so as toincrease the volume of the compression chamber 9, thereby canceling thereduced top clearance and preventing the piston 5 from colliding withthe cylinder head 7.

As described above, the first embodiment provides the oscillation-typecompressor comprising the tightly closed casing 1 having the insidespace 1 a for storing coolant gas, the block 6 accommodated in thetightly closed casing 1, the motor 3 including the stator 3 a and themover 3 b, the piston 5 connected to the mover 3 b of the motor 3, themovable element 12 including the mover 3 b of the motor 3 and the piston5, the stationary element 13 including the stator 3 a of the motor 3 andthe block 6, the elastic element 8 having a portion fixed to the movableelement 12 and another portion fixed to the stationary element 8, thecylinder 4 shiftable in the axial direction with respect the block 6,and the shifting device 16 for shifting the cylinder 4 in the axialdirection. With this arrangement, it becomes possible to minimize thetop clearance adequately in accordance with a given piston stroke. Thecompressor can be always operated with better efficiencies.

Second Embodiment

FIG. 2 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a second embodiment of the presentinvention.

In FIG. 2, the cylinder 4 is put between two stopper projections 17 aand 17 b provided on an inner surface of the block 6 so that thecylinder 4 can shiftable in the axial direction with respect to theblock 6 in a limited range restricted by the stopper projections 17 aand 17 b. Two back-pressure chambers 18 a and 18 b, formed in thetightly closed casing 1 and airtightly partitioned by the integral unitof the cylinder 4 and the cylinder head 7, communicate with the outsidevia back-pressure pipes 19 a and 19 b, respectively. An intake pipe 20directly extends from the cylinder head 7 to the outside of the tightlyclosed casing 1.

A pressure control mechanism 21 is disposed between the back-pressurechambers 19 a, 19 b and intake and exhaust pipes 20 and 10. Morespecifically, the pressure control mechanism 21 comprises a total offour pressure control valves 21 a, 21 b, 21 c and 221 d. Connectingpipes 221 e and 221 f extend from the intake pipe 20 to the pressurecontrol valves 21 a and 21 b, respectively. Connecting pipes 21 g and 21h extend from an exhaust pipe 10 to the pressure control valves 21 c and221 d, respectively. A pressure pipe 21 i connects the pressure controlvalves 21 a and 21 c to the back-pressure pipe 19 a. A pressure pipe 21j connects the pressure control valves 21 b and 221 d to theback-pressure pipe 19 b.

Operation of the oscillation-type compressor in accordance with thesecond embodiment will be explained hereinafter.

The pressure control mechanism 21 introduces the low pressure gas fromthe intake pipe 20 and the high pressure gas from the exhaust pipe 10and adjusts the pressures of the introduced gases by the pressurecontrol valves 21 a, 21 b, 21 c and 221 d to produce adjusted gaseshaving arbitrary pressures in a range from the original high pressure tothe original low pressure. The adjusted gases are supplied into theback-pressure chambers 18 a and 18 b.

When the ambient air temperature is high, an increased cooling power isrequired. In such a case, the pressure control valve 21 c is closedwhile the pressure control valve 21 a is opened. Thus, the back-pressurechamber 18 a is held at a low pressure level.

Meanwhile, the pressure control valve 221 d is opened and the pressurecontrol valve 21 b is closed. Thus, the pressure of the back-pressurechamber 18 b is increased to a high level. The cylinder 4, which isintegral with the cylinder head 7, shifts in the axial direction towardthe stopper projection 17 a due to a pressure imbalance between theback-pressure chambers 18 a and 18 b.

In this case, the top clearance of the piston 5 increases in accordancewith the shift movement of the cylinder 4. However, the increased topclearance can be canceled by applying an increased voltage to the motor3 so as to increase the piston stroke. Thus, the second embodiment makesit possible to maintain the top clearance at a constant value.

Accordingly, it becomes possible to automatically increase the stroke ofthe piston in response to a high ambient air temperature so that thecooling power can be sufficiently obtained even in such a high loadcondition. Thus, efficient compressor operation can be realized inaccordance with the driving conditions of the cooling device withoutusing additional detecting and control devices.

Next, when the ambient air temperature is low, a decreased cooling poweris required. In such a case, the pressure control valve 21 a is closedwhile the pressure control valve 21 c is opened. Thus, the pressure ofthe back-pressure chamber 18 a is increased to a high level.

Meanwhile, the pressure control valve 21 b is opened and the pressurecontrol valve 221 d is closed. Thus, the back-pressure chamber 18 b isheld at a reduced low pressure level. The integral unit of the cylinder4 and the cylinder head 7 shifts in the axial direction toward the otherstopper projection 17 b due to a reversed pressure imbalance between theback-pressure chambers 18 a and 18 b.

In this case, the top clearance of the piston 5 decreases in accordancewith the shift movement of the cylinder 4. However, the decreased topclearance can be canceled by applying a decreased voltage to the motor 3so as to decrease the piston stroke. Thus, the second embodiment makesit possible to maintain the top clearance at the constant value.

Accordingly, it becomes possible to automatically decrease the stroke ofthe piston in response to a low ambient air temperature. Thus, efficientcompressor operation can be realized in accordance with the drivingconditions of the cooling device without using additional detecting andcontrol devices.

As described above, the second embodiment of present invention providesthe oscillation-type compressor comprising the tightly closed casing 1having the inside space 1 a for storing coolant gas, the block 6accommodated in the tightly closed casing 1, the motor 3 including thestator 3 a and the mover 3 b, the piston 5 connected to the mover 3 b ofthe motor 3, the movable element 12 including the mover 3 b of the motor3 and the piston 5, the stationary element 13 including the stator 3 aof the motor 3 and the block 6, the elastic element 8 having one portion8 b fixed to the movable element 12 and another portion 8 c fixed to thestationary element 13, the cylinder 4 shiftable with respect the block6, the cylinder head 7 fixed to the cylinder 4, back-pressure chambers18 a and 18 b formed in the coolant gas space 1 a and airtightlypartitioned by an integral unit including at least one of the cylinder 4and the cylinder head 7, and at least one of the back-pressure chambers18 a, 18 b being held at a low pressure level and another one of theback-pressure chambers 18 a, 18 b being held at a high pressure level.With this arrangement, it becomes possible to realize a practicalcooling device, such as a refrigerator, which is capable ofautomatically increasing the stroke of the piston in response to a highambient air temperature so that the cooling power can be sufficientlyobtained even in the high load condition and is also capable ofautomatically reducing the stroke of the piston in response to adecreased ambient air temperature. Thus, efficient compressor operationcan be realized in accordance with the driving conditions of the coolingdevice without using additional detecting and control devices.

Although the second embodiment of the present invention discloses thepressure control mechanism 21 which controls the pressures in theback-pressure chambers 18 a and 18 b. However, in is needless to saythat similar effects can be obtained even when the pressure controlmechanism 21 is replaced by any other comparable pressure controldevice.

Third Embodiment

FIG. 3 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a third embodiment of the presentinvention.

As shown in FIG. 3, an elastic member 22 resiliently holds or supportsthe integral unit of the cylinder 4 and the cylinder head 7 midwaybetween two stopper projections 17 a and 17 b.

Operation of the oscillation-type compressor in accordance with thethird embodiment will be explained hereinafter.

When a large voltage is suddenly applied to the motor 3, the piston 5may collide with the cylinder head 7. Accordingly, during a start-upoperation of the compressor, the voltage applied to the motor 3 isgradually increased to avoid the collision of the piston 5. In thiscase, the top clearance of the piston gradually decreases with asignificant elapse of time until the pressure conditions of the systemreach the predetermined values.

However, according to the third embodiment of the present invention, theelastic member 22 resiliently holds or supports the cylinder 4 at aposition closer to the top dead center of the piston 5 when thecompressor is stopped. Thus, even when the compressor is driven with asmaller stroke during the start-up operation, the top clearance can bemaintained at a smaller value by the elastic member 22.

Subsequently, the pressure of the compressed air increases and thepiston stroke increases responsively. The cylinder 4 is gradually pushedtoward the stopper projection 17 a by the compression force, while theelastic member 22 resiliently receives or supports the cylinder 4 so asto maintain the top clearance at a constant value. Thus, the pressureconditions of the system can quickly reach the predetermined optimumvalues, realizing efficient compressor operation.

When the compressor is operated stably, the cylinder 4 may oscillatetogether with the piston 5. However, the elastic member 22 acts as adamping means for suppressing the oscillation of the cylinder 4. Thus,the third embodiment reduces the fluctuation of the top clearance of thepiston 5 caused by the co-oscillation between the piton 5 and thecylinder 4, preventing the cooling power from deteriorating.Furthermore, the third embodiment can stabilize the position of thecylinder 4 and suppress the vibration and noise.

As described above, according to the third embodiment of the presentinvention, the oscillation-type compressor comprises the elastic member22 having one end connected to the integral unit of the cylinder 4 andthe cylinder head 7 and the other end connected to the stationaryelement 13. With this arrangement, it becomes possible to suppress thetop clearance of the piston 5 to a small value even in the start-upoperation where the piston is operated at short strokes, therebyrealizing efficient compressor operation. Furthermore, it becomespossible to stabilize the cylinder position during an ordinaryoperation, when compared with a case where the cylinder position iscontrolled by a gas pressure imbalance. Thus, vibration and noise can besuppressed effectively.

Fourth Embodiment

FIG. 4 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a fourth embodiment of the presentinvention.

In FIG. 4, a sensor 23, detecting the position of the piston 5, is fixedto the block 6. Another sensor 24, detecting the position of thecylinder 4, is fixed to the block 6.

A control unit 26 receives the signals produced from the positiondetecting sensors 23 and 24, and controls the pressure control valves 21a, 21 b, 21 c and 21 d.

Operation of the oscillation-type compressor in accordance with thefourth embodiment will be explained hereinafter.

When the stroke of piston 5 increases in response to changed operatingpressure conditions of the compressor, the piston 5 may collide with thecylinder head 7. In this case, the control unit 26 feedback controls thepressure control mechanism 21 based on the signals sent from theposition detecting sensors 23 and 24. More specifically, the pressurecontrol valve 21 c is closed, while the pressure control valve 21 a isopened. Thus, the back-pressure chamber 18 a is held at a low pressurelevel.

Meanwhile, the pressure control valve 221 d is opened and the pressurecontrol valve 21 b is closed. Thus, the back-pressure chamber 18 b isheld at an increased high pressure level. The integral unit of thecylinder 4 and the cylinder head 7 shifts in the axial direction towardthe stopper projection 17 a due to a pressure imbalance between theback-pressure chambers 18 a and 18 b.

In this case, the top clearance of the piston 5 increases in accordancewith the shift movement of the cylinder 4, preventing the piston 5 fromcolliding with the exhaust valve and eliminating noise.

The stroke of the piston 5 decreases in response to the operatingpressure conditions of the compressor. In this case, the oscillationcenter of the piston 5 shifts in a direction opposed to the compressionchamber 9. As a result, the piston 5 cannot reach the top dead centerdue to the shifting of the oscillation center.

The position detecting sensors 23 and 24 continuously monitor thepositions of the piston 5 and the cylinder 4, respectively. When anincreased top clearance is detected based on the signals of the positiondetecting sensors 23 and 24, the controller 26 closes the pressurecontrol valve 21 a and opens the pressure control valve 21 a to hold theback-pressure chamber 18 a at an increased high pressure level.

Meanwhile, the controller 26 opens the pressure control valve 21 b andcloses the pressure control valve 221 d. Thus, the back-pressure chamber18 b is held at a decreased low pressure level. The integral unit of thecylinder 4 and the cylinder head 7 shifts in the axial direction towardthe stopper projection 17 b due to a pressure imbalance between theback-pressure chambers 18 a and 18 b.

In this case, the top clearance of the piston 5 decreases in accordancewith the shift movement of the cylinder 4. Thus, the piston position isalways optimized with respect to the cylinder position. In other words,it becomes possible to minimize the top clearance, preventing thecooling power from deteriorating due to the increase of the topclearance. Efficient compressor operation can be realized.

As described above, according to the fourth embodiment of the presentinvention, the oscillation-type compressor of the present inventioncomprises the cylinder position detecting sensor 24 fixed to one of thestationary element 13 and the cylinder 4. With this arrangement, itbecomes possible to optimize the piston position with respect to thecylinder position irrespective of changed operating pressure conditions,thereby minimizing the top clearance and realizing efficient compressoroperation. Furthermore, it becomes possible to prevent the piston fromcolliding with the exhaust valve when the piston stroke is increased,thereby eliminating any damage and noise.

According to the above-described fourth embodiment, the control unit 26feedback controls the pressure control mechanism 21 to stabilize the topclearance based on the position signals of the piston 5 and the cylinder4. However, it is needless to say that similar effects can be obtainedeven when the feedback control is performed so as to adjust the strokeof the piston 5 by changing the voltage applied to the motor 3 based onthe position signals of the piston 5 and the cylinder 4.

Fifth Embodiment

FIG. 5 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a fifth embodiment of the presentinvention.

In FIG. 5, an auxiliary exhaust pipe 25, slidable in the axialdirection, is coupled with the exhaust pipe 10.

Operation of the oscillation-type compressor in accordance with thefifth embodiment will be explained hereinafter.

When the piston 5 reciprocates in the cylinder 4, the compressorvibrates largely in the axial direction. The caused vibration,transmitted to the stationary element 13 of the compressor, largelyvibrates the exhaust pipe 10 connecting the cylinder head 7 to theoutside of the tightly closed casing 1.

However, according to the fifth embodiment of the present invention, theauxiliary exhaust pipe 25 is coupled with the exhaust pipe 10 andslidable in the axial direction so as to absorb caused vibration. Thus,no vibration is transmitted from the piston 5 to the exhaust pipe 10.

Accordingly, as no vibration is transmitted from the reciprocatingpiston 5 to the exhaust pipe 10, it becomes possible to reduce therepetitive stress applied on the exhaust pipe 10, thereby preventing thereliability from deteriorating due to the damage of the exhaust pipe 10.

As described above, the fifth embodiment of the present inventionprovides the oscillation-type compressor comprising the tightly closedcasing 1 having the inside space la for storing coolant gas, the block 6accommodated in the tightly closed casing 1, the motor 3 including thestator 3 a and the mover 3 b, the piston 5 connected to the mover 3 b ofthe motor 3, the movable element 12 including the mover 3 b of the motor3 and the piston 5, the stationary element 13 including the stator 3 aof the motor 3 and the block 6, the elastic element 8 having one portion8 b fixed to the movable element 12 and another portion 8 c fixed to thestationary element 13, the cylinder 4 fixed to the block 6 or shiftablein the axial direction with respect the block 6, the cylinder head 7fixed to the cylinder 4, the auxiliary pipe 25 having one end shiftablein the axial direction with respect to one of the exhaust pipe 10 andthe intake pipe 20 and the other end fixed to one of the cylinder 4 andthe cylinder head 7. With this arrangement, the exhaust or intake pipecan shift in the axial direction even when large vibration occurs in theaxial direction, thereby reducing the large amplitude stressrepetitively acting on the exhaust or intake pipe. Thus, it becomespossible to prevent the exhaust or intake pipe from being damaged. Evenwhen the cylinder is shifted, it becomes possible to prevent the exhaustor intake pipe from being damaged.

The above-described fifth embodiment discloses the auxiliary exhaustpipe 25 shiftable in the axial direction. However, it is needless to saythat similar effects can be obtained even when a similar arrangement isapplied to the intake pipe 20.

Sixth Embodiment

FIG. 6 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a sixth embodiment of the presentinvention.

In FIG. 6, the oscillation-type compressor comprises a tightly closedcasing 1 having an inside space serving as a coolant gas space 1 a, amain body 2, a motor 3 including a stator 3 a and a mover 3 b, acylinder 122, a piston 5, a yoke 106, a cylinder head 7, an intakechamber 7 a, an exhaust chamber 7 b, and an elastic element 108. Thepiston 5 has one end inserted in a bore of the cylinder 122 and has theother end held by the yoke 106 so as to reciprocate in the axialdirection. A compression chamber 9 is defined by the cylinder 122, thepiston 5 and the cylinder head 7. An exhaust pipe 10 extends from theexhaust chamber 7 b formed in the cylinder head 7 to an outside coolingsystem (not shown). The main body 2 is roughly constituted by a movableelement 112 and a stationary element 121. The movable element 112includes the mover 3 b of the motor 3 and the piston 5. The stationaryelement 121 includes the cylinder 122, the stator 3 a of the motor 3 andthe yoke 106. The main body 2 is elastically supported by a suspensionspring (not shown) in the tightly closed casing 1. The elastic element108 has one end fixed to the movable element 112 and the other end fixedto the stationary element 121. Lubrication oil 11 is stored in the lowerportion of the tightly closed casing 1.

Next, compression mechanism of the above-described oscillation-typecompressor will be explained. First, alternating current of an AC powersource is half-wave rectified and supplied to the stator 3 a. A magneticfield generated by the stator 3 a attracts the mover 3 b fixed to thepiston 5 based on the principle of magnetic variable resistance. Whenthe mover 3 b shifts in the axial direction, the elastic element 108disposed between the mover 3 b and the yoke 106 resiliently deforms inresponse to the shift movement of the piston 5, storing an elastic forcetherein. When the elastic force stored in the elastic element 108 issufficiently increased, the mover 3 b is pushed back to the originalposition. Continuous repetition of this cycle reciprocates the piston 5in the axial direction. In this reciprocative movement, a position ofthe piston 5 nearest to the cylinder head 7 is referred to as a top deadcenter while a position of the piston 5 farthest from the cylinder head7 is referred to as a bottom dead center.

Coolant gas of the cooling system is first introduced into the coolantgas space 1 a in the tightly closed casing 1, and then introduced intothe intake chamber 7 a formed in the cylinder head 7. Subsequently, thecoolant gas enters the compression chamber 9 in the cylinder 4 via anintake valve (not shown) provided in the cylinder head 7. The coolantgas introduced in the compression chamber 9 is compressed by the piston5 which reciprocates in the above-described manner.

The compressed coolant gas. enters the exhaust chamber 7 b of thecylinder head 7 via an exhaust valve (not shown) provided in thecylinder head 7, and is then discharged to the cooling system via theexhaust pipe 10.

Part of the elastic element 108 soaks in the lubrication oil 11. Theelastic element 108 responsive to the reciprocating piston 5 pumps upthe lubrication oil 11. Thus, the lubrication oil 11 is supplied toslide portions of the piston 5 and the yoke 106.

The piston 5 receives a force derived from a pressure imbalance betweenthe compression chamber 9 and the back-surface of the piston 5 inaddition to a spring force of the elastic element 108 and a drivingforce of the motor 3. The oscillation center of the piston 5 shiftstoward the bottom dead center in response to an increased pressure ofthe compression chamber. The oscillation amplitude of the piston 5 isincreased.

In FIG. 6, a block 120, the stator 3 a and the yoke 106 cooperativelyconstitute a stationary element 121. The cylinder 122 is coupled withthe block 120 and slidable along an inner wall of the block 120 so as toreciprocate in the axial direction. An enclosed space 123 is formedbetween the cylinder 122 and the block 120. The piston 5 is coupled withthe cylinder 122 and slidably along a bore wall formed in the cylinder122 so as to reciprocate in the axial direction. A communication passage124, formed in the cylinder 122, has one end connected to the exhaustchamber 7 b and the other end connected to the closed space 123. Aspring 125 interposes between the block 120 and the cylinder 122.

Operation of the oscillation-type compressor in accordance with thesixth embodiment will be explained hereinafter.

High-pressure coolant gas, compressed in the compression chamber 9during the compressing operation of the compressor, is sent to theexhaust chamber 7 b and then discharged to the cooling system via theexhaust pipe 10. At the same time, part of the pressurized coolant gasis introduced into the closed space 123 via the communication passage124. The cylinder 122 receives a force derived from a pressure imbalancebetween the closed space 123 and the tightly closed casing 1. Thecylinder 122 shifts toward the top dead center and stops at a balancedpoint where the force caused by the pressure imbalance balances with thespring force of the spring 125.

When the ambient temperature is high, the pressure of the closed space123 increases to a higher level. Thus, the cylinder 122 shifts towardthe top dead center than the usual position. By adjusting the motorpower, the volume of the compression chamber 9 at the top dead center ismaintained at the same value. The top dead center position of the piston5 shifts away from the neutral position of the elastic element 108.Accordingly, the bottom dead center position shifts in the oppositedirection with respect to the neutral position of the elastic element108. As a result, the piston stroke increases and the exhaust amount ofthe coolant gas increases. The cooling power increased.

Furthermore, the sixth embodiment can reduce an area contacting withhigh-pressure gas compared with a case where the cylinder shifts inresponse to the high pressure acting on the entire back surface of thecylinder. This is effective to reduce the thermal loss.

Furthermore, under a condition where the cylinder receives a highpressure at its entire back surface, it is impossible to supplylow-pressure lubrication oil from the bottom of the tightly closedcasing to a high-pressure slide portion. However, according to the sixthembodiment, the high-pressure portion is limited to a smaller space.Thus, the lubrication oil can be pumped up by the movement of theelastic element soaked in the lubrication oil and supplied to the slideportions of the piston and the yoke.

As described above, the sixth embodiment of the present inventionprovides the oscillation-type compressor comprising the block 120 andthe piston 5 accommodated in the tightly closed casing 1, the motor 3including the stator 3 a and the mover 3 b, the movable element 112including the mover 3 a and the piston 5, the stationary element 121including the block 120 and the stator 3 a, the elastic element 108having a portion fixed to the movable element 112 and another portionfixed to the stationary element 121, the cylinder 122 accommodating thepiston 5 so that the piston 5 is shiftable in the axial direction, thecylinder 122 being inserted in the block 120 so as to reciprocate in theaxial direction with the closed space 123 formed between the block 120and the cylinder 122, the cylinder head 7 comprising the exhaust chamber7 b and attached to the cylinder 122, and the communication passage 124connecting the closed space 123 and the exhaust chamber 7 b. With thisarrangement, it becomes possible to increase the piston stroke bycausing the cylinder to shift toward the top dead center in response tothe increased high pressure of the space when the ambient temperature ishigh and therefore the required cooling power is high. Thus, the coolingpower can be increased. Furthermore, this arrangement can reduce an areacontacting with high-pressure gas compared with a case where thecylinder shifts in response to the high pressure acting on the entireback surface of the cylinder. This is effective to reduce the thermalloss. Furthermore, according to this arrangement, the lubrication oilstored in the lower part of the tightly closed casing can be pumped upby the movement of the movable element. Thus, the lubrication oil can beeasily supplied to the slide portions, with reduced slide loss andeliminated wear.

According to the above-described sixth embodiment, the spring isdisposed between the cylinder and the block. However, it is needless tosay that the similar effects will be obtained when the spring isreplaced by a comparable element, such as a magnet, capable ofgenerating a reaction force for varying the cylinder position inresponse to the changed pressure of the space.

Furthermore, the cylinder 122 is subjected to a variable load inaccordance with the changed pressure of the compression chamber 9 duringone stroke. This variable load may shift the cylinder 122 widely,reducing the volume of the compression chamber 9 at the bottom deadcenter and deteriorating the cooling power. Therefore, it is preferablethat the cross section of the closed space 123 is sufficiently largerthan that of the compression chamber 9. Furthermore, to suppress theshift amount of the cylinder during one stroke, it is preferable to usethe spring 125 having a large spring coefficient.

Seventh Embodiment

FIG. 7 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a seventh embodiment of the presentinvention.

In FIG. 7, an exhaust pipe 126 extends from the closed space 123 to thecooling system located outside the compressor.

The seventh embodiment comprises the exhaust pipe 126 in addition to thearrangement of the sixth embodiment. According to the seventhembodiment, the exhaust chamber 7 b communicates with the cooling systemvia the closed space 123.

Operation of the oscillation-type compressor in accordance with theseventh embodiment will be explained hereinafter.

The high-pressure coolant gas, compressed in the compression chamber 9during the compressing operation of the compressor, is sent to theexhaust chamber 7 b and then discharged to the closed space 123 via thecommunication passage 124. The closed space 123 acts as a muffler forreducing the flowing speed of the discharged coolant gas. Thedecelerated coolant gas is then sent to the cooling system via theexhaust pipe 126.

The amount of the coolant gas discharged from the compression chamber 9increases in accordance with an increased ambient temperature. However,the volume of the closed space 123 increases in response to theincreased exhaust gas amount so as to suppress the pulsation in theclosed space 123, thereby preventing noise and vibration.

As described above, the seventh embodiment of the present inventionprovides the oscillation-type compressor further comprising the exhaustpipe 126 connecting the closed space 123 and the cooling system. Withthis arrangement, the coolant gas compressed in the compression chamber9 is once expanded in the closed space 123 and then discharged to thecooling system. Accordingly, when the exhaust gas amount increases inresponse to an increased stroke, the volume of the closed space 123increases correspondingly so as to act as a muffler. Thus, the pulsationis surely reduced, while noise and vibration can be suppressed.

Eighth Embodiment

FIG. 8 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with an eighth embodiment of the presentinvention.

In FIG. 8, a radially extending passage 128 is provided in the block120. A radially outer end 128 a of the passage 128 is connected to thelower part of the closed space 123. A radially inner end 128 b isconnected to a ring groove 128 c extending along the slide surfacebetween the cylinder 122 and the block 120.

The eighth embodiment differs from the seventh embodiment in that thepassage 128 is additionally provided.

Operation of the oscillation-type compressor in accordance with theeighth embodiment will be explained hereinafter.

The high-pressure coolant gas, compressed in the compression chamber 9during the compressing operation of the compressor, is sent into theexhaust chamber 7 b and then discharged to the closed space 123 via thecommunication passage 124. The flowing speed of the coolant gas isreduced in the closed space 123 so that the lubrication oil mistcontained in the decelerated coolant gas falls by gravity and gathers atthe bottom of the closed space 123. The lubrication oil thus stored inthe lower part of the closed space 123 is pumped up via the radiallyextending passage 128 from the one end 128 a to the other end 128 b andsupplied to the ring groove 128 c. The supplied lubrication oillubricates the entire slide surface between the cylinder 122 and theblock 120. Thus, the clearance between the cylinder 122 and the block120 is completely sealed by the lubrication oil so as to improveairtightness. Thus, it becomes possible to eliminate leaking loss.Furthermore, forming an oil film between the cylinder 122 and the block120 prevents any wear occurring at the slide surface between thecylinder 122 and the block 120.

As described above, the eighth embodiment of the present inventionprovides the oscillation-type compressor further comprising the passage128 connecting the slide surface between the cylinder 122 and the block120 and the bottom of the closed space 123. With this arrangement, itbecomes possible to supply lubrication oil from the bottom of the closedspace 123 to the slide surface between the cylinder 122 and the block120 via the passage 128. Thus, the slide surface is airtightly sealed bythe supplied lubrication oil. It becomes possible to prevent the coolantgas from leaking from the closed space. Supplying the lubrication oil tothe slide surface can prevent the cylinder and the block from wearing.

Ninth Embodiment

FIG. 9 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a ninth embodiment of the presentinvention. FIG. 10 is a vertical cross-sectional view showing anoperated condition of the oscillation-type compressor in accordance withthe ninth embodiment.

In FIGS. 9 and 10, a combined groove 130 is provided on a slide surfaceof the cylinder 122 or the block 120. A groove 130 a is provided on thecylinder 122, and another groove 130 b is provided on the block 120. Acommunication passage 131 has one end 131 a connected to the exhaustchamber 7 b of the cylinder head 7 and another end 131 b facing thegroove 130 b formed on the cylinder 122.

The ninth embodiment differs from the sixth embodiment in that thecommunication passage 124 is omitted and the groove 130 and thecommunication passage 131 are additionally provided.

Operation of the oscillation-type compressor in accordance with theninth embodiment will be explained hereinafter.

The high-pressure coolant gas, compressed in the compression chamber 9during the compressing operation of the compressor, is sent into theexhaust chamber 7 b and then discharged to the cooling system via theexhaust pipe 10. At the same time, part of the pressurized coolant gasis introduced into the closed space 123 via the communication passage131 and the groove 130 b. When the ambient temperature increases, thepressure of the closed space 123 increases to a higher level. Thecylinder 122 receives an increased pressure of the closed space 123 andshifts toward the top dead center. The piston 5 has an increased stroke.

However, when the system is in an unstable start-up condition or whenthe ambient temperature is extraordinarily increased, the exhaustpressure may increase extraordinarily to shift the cylinder 122excessively toward the top dead center. However, according to the ninthembodiment of the present invention, when the cylinder 122 shifts towardthe top dead center, the open end 131 b of the communication passage 131is dislocated from the groove 130 b so as to disconnect the closed space123 from the exhaust chamber 7 b. Accordingly, introduction of thehigh-pressure coolant gas into the closed space 123 is stopped. At thesame time, the closed space 123 communicates with the inside space ofthe tightly closed casing 1 via the groove 130 a so as to discharge thecoolant gas out of the closed space 123. As a result, the pressure levelof the closed space 123 is reduced. The movement of the cylinder 122shifting toward the top dead center is suppressed within a predeterminedrange. Thus, it becomes possible to prevent the piston stroke fromexcessively increasing, while causing no problems in the reliability ofthe elastic element or the like.

As described above, the ninth embodiment of the present inventionprovides the oscillation-type compressor further comprising the combinedgroove 130 provided on the slide surface of one of the cylinder 122 andthe block 120. With this arrangement, when the cylinder 122 widelyshifts toward the top dead center, the groove 130 acts as a means fordischarging the pressurized gas from the closed space 123 so that thepiston stroke can be maintained within a predetermined range.Accordingly, it becomes possible to prevent the piston stroke fromexcessively increasing, while causing no problems in the reliability ofthe elastic element or the like.

Tenth Embodiment

FIG. 11 is a view showing an arrangement of an oscillation-typecompressor in accordance with a tenth embodiment of the presentinvention. FIG. 12 is a view showing characteristics of theoscillation-type compressor in accordance with the tenth embodiment ofthe present invention.

In FIG. 11, the oscillation-type compressor comprises a tightly closedcasing 1 and a main body 2. The tightly closed casing 1 has an insidespace serving as a coolant gas space 1 a. A motor 3 includes a stator 3a and a mover 3 b. The mover 3 b is fixed to a piton 5. The main body 2is roughly constituted by a movable element 12 and a stationary element13. The movable element 12 includes the mover 3 b of the motor 3 and thepiston 5. The stationary element 13 includes a cylinder 4, the stator 3a of the motor 3 and a block 6. The main body 2 is elastically supportedby a suspension spring (not shown) in the tightly closed casing 1.Lubrication oil 11 is stored in the lower portion of the tightly closedcasing 1.

The cylinder 4 and an elastic element 8 cooperatively support the piston5 so as to be slidable and reciprocate in the axial direction. Acompression chamber 9 is defined by the cylinder 4 and the piston 5.

A piston position detecting sensor 214, constituted by a differentialtransformer including a coil 214 a and a core 214 b, detects theposition of the piston 5 and generates an analog signal representing thesame. This analog signal is converted into a digital signal by an A/Dconverter 215, and then supplied to a top dead center positioncalculator 216. An output of the top dead center position calculatingunit 216 is supplied to a reciprocative movement controller 221 providedin an amplitude controller 218. An output of the reciprocative movementcontroller 221 is sent to a base drive circuit 222 which is connected toa power source 217.

Furthermore, the reciprocative movement controller 221 comprises acomparator 224 comparing the top dead center position signal generatedfrom the top dead center position calculating device 216 with a top deadcenter reference value 219 stored in a memory (not shown) in theamplitude controller 218, and an amplifier 220 changes the amplitude ofan output voltage sent to a base drive circuit 222.

Next, compression mechanism of the above-described oscillation-typecompressor will be explained. First, alternating current of a commercialAC power source is supplied to the motor via the power source 217. Amagnetic field generated by the stator 3 a attracts the mover 3 b fixedto the piston 5 based on the principle of magnetic variable resistance.When the mover 3 b shifts in the axial direction, the elastic element 8disposed between the mover 3 b and the block 6 resiliently deforms inresponse to the shift movement of the piston 5, storing an elastic forcetherein. When the elastic force stored in the elastic element 8 issufficiently increased, the mover 3 b is pushed back to the originalposition. Continuous repetition of this cycle reciprocates the piston 5in the axial direction.

The position of the piston 5, detected by the piston position detectingsensor 214 as an analog signal, is converted into a digital signal bythe A/D converter 215 and supplied to the top dead center positioncalculating device 216 to obtain a top dead center position “A.” Thecalculated top dead center position “A” is compared with the top deadcenter reference value 219. The amplifier 220 controls the amplitude ofthe output voltage supplied to the base drive circuit 222 in accordancewith a comparison result so as to eliminate the difference between thecalculated top dead center position “A” and the top dead centerreference value 219. Accordingly, the piston 5 continuously repeats thereciprocative movement while keeping a constant top dead centerposition.

Coolant gas of a cooling system (not shown) is introduced into alow-pressure chamber 7 a of a cylinder head 7, and then enters acompression chamber 9 of the cylinder 4 via an intake valve (not shown)disposed in the cylinder head 7. The coolant gas introduced in thecompression chamber 9 is compressed by the piston 5 which reciprocatesin the above-described manner.

The compressed coolant gas enters a high-pressure chamber 7 b of thecylinder head 7 via an exhaust valve (not shown) disposed in thecylinder head 7, and then exits the cylinder head 7 to the coolingsystem.

Furthermore, a top dead center reference value changing device 223 isprovided to change the top dead center reference value 219 in accordancewith varied ambient air temperature and the pressure and load conditionsof a cooling system (not shown).

Operation of the oscillation-type compressor in accordance with thetenth embodiment will be explained hereinafter.

During a compressing operation of the compressor, the output voltage ofthe power source 217 is feedback controlled in accordance with adifference between the measured top dead center position of the piston 5and the top dead center reference value 219 preset in the amplitudecontroller 218 so as to eliminate the difference, thereby maintaining aconstant top clearance.

However, the required cooling power reduces in response to changedexternal conditions, such as a reduced ambient air temperature and areduced thermal load. In this case, the top dead center reference valuechanging device 223 selects a preferable value from a plurality ofpre-memorized top dead center reference values in accordance with therequired cooling power. Thus, the cooling power is variable inaccordance with the varied external conditions relating to the ambientair temperature, the system pressure, the system temperature etc.

Thus, the above-described tenth embodiment increases the top clearanceso as to suppress the cooling power of the compressor. This makes itpossible to adjust the cooling power of the compressor in accordancewith the required power of the cooling system, thereby preventing thecooling power from excessively increasing and realizing the efficientcompressor operation.

FIG. 12 is a graph showing experimental data obtained by the inventors.As apparent from FIG. 12, the cooling power decreases with increasingtop clearance of the piston 5 corresponding to the increased top deadcenter reference value 219. The compressor efficiency is substantiallyconstant when a ratio of the top clearance volume to the cylinder volumeis within 10%. However, the compressor efficiency starts decreasing whenthe ratio of the top clearance volume to the cylinder volume exceeds10%.

As apparent from the experimental data shown in FIG. 12, the tenthembodiment makes it possible to reduce the cooling power toapproximately 50% without deteriorating the compressor efficiency or thecooling system efficiency when the ratio of the top clearance volume tothe cylinder volume is within 10%. Thus, it becomes possible to drivethe compressor at an optimized power level in accordance with externalconditions.

As described above, the tenth embodiment of the present inventionprovides the oscillation-type compressor comprising the tightly closedcasing 1 having an inside space 1 a for storing coolant gas, thecylinder 4 accommodated in the tightly closed casing 1, the motor 3including the stator 3 a and the mover 3 b, the piston 5 connected tothe mover 3 b of the motor 3, the movable element 12 including the mover3 b of the motor 3 and the piston 5, the stationary element 13 includingthe stator 3 a of the motor 3 and the cylinder 4, the elastic element 8having a portion 8 b fixed to the movable element 12 and another portion8 c fixed to the stationary element 13, the piton position detectingsensor 214 detecting the position of the piston 5, the top dead centerposition calculating means 216 for calculating the top dead centerposition of the piston 5 based on the piston position signal obtainedfrom the piton position detecting sensor 214, the amplitude controlmeans 218 for controlling the amplitude of the mover 3 b in accordancewith a difference between the top dead center position and a selectedtop dead center reference value 219, and the top dead center referencevalue changing means 223 for changing the top dead center referencevalue 219. With this arrangement, the top clearance of the piston 5 canbe increased in response to a decreased ambient air temperature or areduced load. Thus, the cooling power is suppressed withoutdeterioration of the compressor efficiency. Thus, it becomes possible torealize an efficient compressor operation in accordance with the ambientair temperature change or the load change.

According to the above-described tenth embodiment, the motor 3 comprisesthe stator 3 a and the mover 3 b. However, it is needless to say thatthe similar effects will be obtained even when the motor 3 is replacedby a different motor which is capable of causing the piston 5 toreciprocate in the same manner.

Eleventh Embodiment

FIG. 13 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with an eleventh embodiment of the presentinvention.

In FIG. 13, a movable stator base 227 is fixed to the stator 3 a of themotor 3. The movable stator base 227 is coupled with the block 6 andshiftable in the axial direction with respect to the block 6. Themovable stator base 227 and the block 6 cooperatively define twoback-pressure chambers 228 a and 228 b located at both ends of themovable stator base 227 and communicated with the outside of the tightlyclosed casing 1. The back-pressure chambers 228 a and 228 b communicatewith the outside of the tightly closed casing 1 via back-pressure pipes226 b and 226 b, respectively. An intake pipe 20 extends from theoutside of the tightly closed casing 1 to the cylinder head 7.

A pressure control mechanism 225 comprises a total of four pressurecontrol valves 225 a, 225 b, 225 c and 225 d. Connecting pipes 225 e and225 f extend from the intake pipe 20 to the pressure control valves 225a and 225 b, respectively. Connecting pipes 225 g and 225 h extend froman exhaust pipe 10 to the pressure control valves 225 c and 225 d,respectively. A pressure pipe 225 i connects the pressure control valves225 a and 225 c to the back-pressure pipe 226 b. A pressure pipe 225 jconnects the pressure control valves 225 b and 225 d to theback-pressure pipe 226 a.

The pressure control mechanism 225 introduces the low pressure gas fromthe intake pipe 20 and the high pressure gas from the exhaust pipe 10and adjusts the introduced high and low pressure gases by the pressurecontrol valves 225 a, 225 b, 225 c and 225 d to produce adjusted gaseshaving arbitrary pressures in a range from the introduced original highand low pressures.

Operation of the oscillation-type compressor in accordance with theeleventh embodiment will be explained hereinafter.

The oscillation center of the piston 5 shifts toward the compressionchamber 9 in response to changed operating pressure conditions, such asa decreased ambient air temperature and a reduction of the gas pressure.The piston 5 may exceed the top dead center position and collide withthe cylinder head 7.

In this case, the pressure control valve 225 d is opened and thepressure control valve 225 b is closed. Thus, the back-pressure chamber228 a is held at the high pressure. Furthermore, the pressure controlvalve 225 c is closed and the pressure control valve 225 a is opened.Thus, the back-pressure chamber 228 b is held at the low pressure.

The movable stator base 227 and the stator 3 a shift together toward ananti-compression side surface 6 b of the block 6, i.e., in a directionopposed to the compression chamber 9 due to a pressure imbalance betweenthe back-pressure chambers 228 a and 228 b.

Accordingly, the oscillation center of the piston 5 shifts in thedirection opposed to the compression chamber 9 in response to the shiftmovement of the stator 3 a of the motor 3. The top dead center positionof the piston 5 also shifts in the direction opposed to the compressionchamber 9. Thus, it becomes possible to prevent the piston 5 fromcolliding with the cylinder head 7, eliminating vibration and noise.

As described above, the eleventh embodiment of the present inventionprovides the oscillation-type compressor comprising the tightly closedcasing 1 having the inside space 1 a for storing coolant gas, thecylinder 4 and the block 6 accommodated in the tightly closed casing 1,the motor 3 including the stator 3 a and the mover 3 b, the piston 5connected to the mover 3 b of the motor 3, the movable element 12including the mover 3 b of the motor 3 and the piston 5, the stationaryelement 13 including the stator 3 a of the motor 3, the cylinder 4 andthe block 6, the elastic element 8 having a portion 8 b fixed to themovable element 12 and another portion 8 c fixed to the stationaryelement 13, the stator 3 a of the motor 3 or a movable stator base 227connected to the stator 3 a being partly coupled with the stationaryelement 13 so as to reciprocate in the axial direction in response to apressure imbalance between back-pressure chambers 228 a and 228 b formedtherebetween, and the pressure control mechanism 225 for controlling thepressures of the back-pressure chambers 228 a and 228 b. With thisarrangement, the stator of the motor shifts in a direction opposed tothe compression chamber when the top dead center position of the pistonshifts toward the cylinder head in response to changed operatingpressure conditions. Accordingly, the oscillation center of the pistonshifts in the direction opposed to the compression chamber. Thus, itbecomes possible to prevent the piston from colliding with the exhaustvalve, eliminating vibration and noise.

Although the above-described eleventh embodiment discloses the pressurecontrol mechanism 225 which controls the pressures of the back-pressurechambers 228 a and 228 b. However, it is needless to say that similareffects can be obtained even when the pressure control mechanism 225 isreplaced by any other comparable pressure control device or a comparablemechanism for shifting the movable stator base 227 integrated with thestator 3 a of the motor 3.

According to the above-described eleventh embodiment, the motor 3comprises the stator 3 a and the mover 3 b. However, it is needless tosay that the similar effects will be obtained even when the motor 3 isreplaced by a different motor which is capable of causing the piston 5to reciprocate in the same manner.

Twelfth Embodiment

FIG. 14 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a twelfth embodiment of the presentinvention.

In FIG. 14, a shifting element 229 is provided for shifting the stator 3a in the axial direction, in addition to the arrangement of the eleventhembodiment.

Operation of the oscillation-type compressor in accordance with thetwelfth embodiment will be explained hereinafter.

When the compressor is started up, the piston 5 causes a reciprocativemovement in accordance with the current supplied to the motor 3.However, the compression chamber 9 is held at a low pressure immediatelyafter the start-up operation of the compressor. Accordingly, the gaspressure acting on the piston 5 is so small that the piston 5 cannotshift sufficiently in the direction opposed to the compression chamber9. In other words, the oscillation center of the piston 5 is dislocatedtoward the compression chamber 9. This may cause the piston 5 to collidewith the exhaust valve of the cylinder head 7. However, according to thetwelfth embodiment of the present invention, the shifting element 229shifts the stator 3 a of the motor 3 in the direction opposed to thecompression chamber 9. Thus, during the start-up operation of thecompressor, the oscillation center of the piston 5 can be positionedsufficiently far from the compression chamber 9.

Accordingly, it becomes possible to prevent the piston 5 from collidingwith the cylinder head 7 during the start-up operation of thecompressor, preventing the exhaust valve from being damaged andeliminating noise and vibration.

As described above, the twelfth embodiment of the present inventionprovides the oscillation-type compressor comprising the shifting means229 for shifting the stator 3 a of the motor 3 in a direction opposed tothe compression chamber 9 when the compressor is stopped. With thisarrangement, the motor stator shifts in the direction opposed to thecompression chamber when the compressor is stopped. As the oscillationcenter of the piston during the start-up condition is shifted far fromthe compression chamber compared with that of the ordinary drivingcondition, it becomes possible to prevent the piston from colliding withthe exhaust valve during the start-up operation, eliminating vibrationand noise.

According to twelfth embodiment, the shifting element 229 is made of aspring. However, it is needless to say that the similar effects will beobtained even when the spring is replaced by any other comparableelement which is capable of shifting the stator 3 a in the axialdirection.

Thirteenth Embodiment

FIG. 15 is a cross-sectional view showing an oscillation-type compressorin accordance with a thirteenth embodiment of the present invention.FIG. 16 is a diagram showing an electric circuit of the oscillation-typecompressor in accordance with the thirteenth embodiment of the presentinvention.

In FIGS. 15 and 16, the oscillation-type compressor comprises a mainbody 301, a block 302, a motor 3 including a magnet serving as a stator3 a and a coil serving as a mover 3 b, a cylinder 4, and a piston 5. Acylinder head 7 comprises an intake valve 307 a and an exhaust valve 307b. The piston 5 is accommodated in the cylinder 4, so that the piston 5reciprocates in an axial direction. The cylinder 4, the piston 5 and thecylinder head 7 cooperatively define a compression chamber 9. Thecompression chamber 9 is connected to an external cooling circuit (notshown) via an intake pipe 20 and an exhaust pipe 10.

The main body 301 is roughly constituted by a movable element 12 and astationary element 13. The movable element 12 includes the piston 5 andthe mover 3 b of the motor 3. The stationary element 13 includes thecylinder 4 and the stator 3 a of the motor 3. The main body 301 iselastically supported by a suspension spring (not shown) in the tightlyclosed casing (not shown). Each elastic element 314 has one end fixed tothe movable element 12 and the other end fixed to the stationary element13. A displacement detector 319 includes a core 319 a and a coil 319 b.The core 319 a is connected to the movable element 12 via a connectingmember 315 extending in the axial direction. The coil 319 b is fixed tothe stationary element 13 and has an inside space for accommodating thecore 319 a.

Coolant gas of the cooling system is introduced into the compressionchamber 9 via the intake pipe 20 and the intake valve 307 a. The coolantgas introduced in the compression chamber 9 is compressed by the piston5 which reciprocates in the above-described manner. The compressedcoolant gas is discharged via the exhaust valve 307 b and the exhaustpipe 10 to the cooling system.

Next, compression mechanism of the above-described oscillation-typecompressor will be explained. An inverter circuit 341 generates AC powerwhich is supplied to the coil of the mover 3 b fixed to the piston 5. Anexited coil of the stator 3 a generates a magnetic field. Beingattracted in a direction crossing the magnetic field, the mover 3 breciprocates in the axial direction. The elastic element 314 resilientlydeforms in response to the shift movement of the movable element 12,storing an elastic force therein. When the elastic force stored in theelastic element 314 is sufficiently increased, the movable element 12 ispushed back to the original position. Continuous repetition of thiscycle reciprocates the piston 5 in the axial direction.

It is preferable that the frequency of the AC power generated by theinverter circuit 341 is equal to the resonant frequency of the systemwhich is determined by the mass of the movable element 12 and a springcoefficient of the elastic element 314. With this setting, it becomespossible to effectively use the spring force of the elastic element 314to cause the movable element 12 self-reciprocating.

Only when the piston 5 is positioned in the vicinity of the top deadcenter, the core 319 a and the coil 319 b cooperatively detect adisplacement. Thus, the displacement detector 319 solely detects the topdead center position of the piston 5. A top dead center positiondetector 320 is provided for calculating the top dead center of thepiston 5 based on a signal obtained from the displacement detector 319.

A current/voltage detector 321 is provided for detecting current flowingacross the motor 3 or voltage applied to the motor 3. A power supplier322 is provided for changing the voltage applied to the motor 3 based onoutput signals of the top dead center position detector 320 and thecurrent/voltage detector 321.

Operation of the oscillation-type compressor in accordance with thethirteenth embodiment will be explained.

The movable element 12 reciprocates together with the core 319 a of thedisplacement detector 319. The core 319 a is short because the detectionrange of the displacement detector 319 is limited to the vicinity of thetop dead center of the piston 5. Accordingly, an overall weight of themovable element 12 including the core 319 a is reduced, while theresonance frequency is increased and therefore an increased coolingpower is obtained. Furthermore, reducing the weight of the reciprocatingunit including the movable element 12 is effective to suppress thevibration.

Furthermore, limiting the detection range of the displacement detector319 to the vicinity of the top dead center is effective to eliminateadverse influence of error factors and to accurately detect the positionof the piston 5. The power supplier 322 decreases the output voltage ofthe inverter circuit 341 when the detected top dead center position islarger than a reference top dead center position and increases theoutput when the detected top dead center position is smaller than thereference top dead center position. Through this feedback control, thetop dead center position of the piston 5 can be equalized to thereference top dead center. As the displacement detector 319 has highdetection accuracy, it becomes possible to reduce and stabilize thedeviation of the top dead center position with respect to the referencetop dead center position. A small top clearance is obtained by settingan adequate reference top dead center position. Thus, the coolingability is increased. The capability of accurately detecting the topdead center makes it possible to prevent the piston 5 from collidingwith the cylinder head 7. Thus, it becomes possible to suppresscollision noise and prevent the valve from being damaged.

Furthermore, the current/voltage detector 321 monitors current orvoltage. This makes it possible to calculate the amplitude of the piston5 based on the monitored current or voltage. Furthermore, the bottomdead center position is obtained by adding the calculated amplitude tothe top dead center position detected by the top dead center positiondetector 320. Based on this result, the power supplier 322 decreases thevoltage applied to the motor 3 when the obtained amplitude exceeds apreset value. Accordingly, it becomes possible to prevent the movableelement 12 from oscillating with an excessively large amplitude,preventing the movable element 12 from colliding with the stationaryelement 13, and preventing the elastic element 314 from beingexcessively deformed and damaged.

As described above, the thirteenth embodiment of the present inventionprovides the oscillation-type compressor comprising the block 302 andthe piston 5, the motor 3 including the stator 3 a and the mover 3 b,the movable element 12 including the mover 3 b and the piston 5, thestationary element 13 including the block 302 and the stator 3 a, theelastic element 314 having a portion fixed to the movable element 12 andanother portion fixed to the stationary element 13, the cylinder 4accommodating the piston 5 so as to allow the piston 5 reciprocating inthe axial direction, the displacement detector 319 connected to thepiston 5 in the axial direction for detecting the position near the topdead center of the piston 5, the top dead center position detectingmeans 320 for obtaining the top dead center position of the piston 5based on. the signal obtained from the displacement detector 319, thecurrent/voltage detecting means 321 for detecting the current or voltagevalue of the motor 3, and the power supply means 322 for changing thevoltage applied to the motor 3 based on output signals of the top deadcenter position detecting means 320 and the current/voltage detectingmeans 321. According to this arrangement, the displacement detector isonly used for detecting the position near the top dead center of thepiston. Downsizing the displacement detector is easy compared with thecase where the displacement detector is used for detecting the entireamplitude of the piston. The movable element is light. The resonancefrequency can be increased, while an increased cooling power isobtained.

Furthermore, as the usage of the displacement detector is limited to thedetection of the position near the piston top dead center, it becomespossible to accurately detect the top dead center compared with the casewhere the displacement detector is used for detecting the entireamplitude. It becomes possible to suppress the fluctuation of the topclearance, thereby providing a reduced top clearance. The cooling poweris increased, while it becomes possible to prevent the piston fromcolliding with the cylinder head. Furthermore, as the movable element islight due to the downsized displacement detector, it becomes possible tosuppress the vibration caused by the reciprocative movement of themovable element. The piston amplitude detection is realized by detectingthe current or voltage. It becomes possible to prevent the piston fromoscillating with an excessively large amplitude, while preventing themovable element from colliding with the stationary element. Thereliability of the elastic element can be maintained adequately so asnot to be deteriorated by the excessive oscillation.

Fourteenth Embodiment

FIG. 17 is a cross-sectional view showing an oscillation-type compressorin accordance with a fourteenth embodiment of the present invention.

In FIG. 17, a displacement detector 325 is disposed inside the stator 3a of the motor 3. A cylindrical core 325 a is inserted in a recessformed on a slide surface of a piston 5. A coil 325 b is inserted in arecess formed on a slide surface of a cylinder 4.

Operation of the oscillation-type compressor in accordance with thefourteenth embodiment will be explained. The core 325 a of thedisplacement detector 325 is directly fixed to the piston 5 of themovable element 12. In other words, this arrangement requires noconnecting parts used for fixing the displacement detector 325 to themovable element 12. Thus, the movable element 12 is light. The resonancefrequency is increased, while the cooling power is increased. Theweight-reduced movable element effectively eliminates the vibrationcaused by the reciprocative movement of the movable element.

The fourteenth embodiment disposes the displacement detector 325 midwayon each slide surface of the piston 5 and the cylinder 4. However, it isneedless to say that similar effects will be obtained when thedisplacement detector is located at an appropriate portion radiallyinward than the motor 3.

As described above, the fourteenth embodiment of the present inventionprovides the oscillation-type compressor comprising the block 302 andthe piston 5, the motor 3 including the stator 3 a and the mover 3 b,the movable element 12 including the mover 3 b and the piston 5, thestationary element 13 including the block 302 and the stator 3 b, theelastic element 14 having a portion fixed to the movable element 12 andanother portion fixed to the stationary element 13, the cylinder 4accommodating the piston 5 so as to allow the piston 5 reciprocating inthe axial direction, and the displacement detector 325 attached to themovable element 12 and the stationary element 13 at a radially inwardportion with respect to the stator 3 a of the motor 3. This arrangementrequires no connecting parts used for fixing the displacement detectorto the movable element. Thus, the movable element is light. Theresonance frequency can be improved, while the cooling power isincreased. The weight reduced movable element effectively eliminates thevibration caused by the reciprocative movement of the movable element.

Fifteenth Embodiment

FIG. 18 is a cross-sectional view showing an oscillation-type compressorin accordance with a fifteenth embodiment of the present invention. FIG.19 is a cross-sectional view showing an essential arrangement of theoscillation-type compressor in accordance with the fifteenth embodimentof the present invention.

In FIGS. 18 and 19, a spiral elastic element 330 has a radially innerportion 330 a fixed to a movable element 12. A radially outer portion330 b of the spiral elastic element 330 is slidably put betweenprojections 333 a and 333 b protruding from an inner cylindrical wall ofa block 302 of a stationary element 13. Thus, the spiral elastic element330 is rotatably supported about a shaft of a piston 5. A dynamicpressure generating mechanism 334, comprising a plurality of recesses334 a, is provided on a slide surface between the piston 5 and acylinder 4. A rotational direction restricting mechanism 337 comprises aratchet wheel 337 a formed along the radially outer portion 330 b and aclick 337 b fixed to the inner cylindrical surface of the block 302 in acantilever fashion so as to form a ratchet drive arrangement between theratchet wheel 337 a and the click 337 b. The rotational directionrestricting mechanism 337 limits the rotational direction of the elasticelement 330 in the counterclockwise direction.

Operation of the oscillation-type compressor in accordance with thefifteenth embodiment will be explained.

During the compressing operator of the compressor, the radially innerportion 330 a of the elastic element 330 shifts in the axial directionof the piston 5 in response to the reciprocative movement of the movableelement 12. Meanwhile, the reciprocative movement of the movable element12 causes a significant rotational displacement between the radiallyinner portion 330 a and the radially outer portion 330 b due to thespiral configuration of the elastic element 330. More specifically, alarge displacement of the elastic element 330 causes a clockwiserotational displacement, while a small displacement of the elasticelement 330 causes a counterclockwise rotational displacement.

When the radially inner portion 330 a of the elastic element 330 rotatesin the counterclockwise direction with respect to the radially outerportion 330 b, the rotational direction restricting mechanism 337 locksthe radially outer portion 330 b by engagement between the ratchet wheel337 a and the click 337 b. As a result, the movable element 12 integralwith the radially inner portion 330 a of the elastic member 330 rotatesin the counterclockwise direction. On the other hand, when the radiallyinner portion 330 a of the elastic element 330 rotates in the clockwisedirection with respect to the radially outer portion 330 b, therotational direction restricting mechanism 337 allows the radially outerportion 330 b to rotate freely. As a result, the radially outer portion330 b of the elastic element 330 having an inertia moment smaller thanthat of the piston 5 rotates in the counterclockwise direction.

Accordingly, the piston 5 of the movable element 12 always rotates inthe counterclockwise direction.

A plurality of triangular recesses 334 a, serving as the hydraulicpressure generating mechanism 334, are formed on a slide surface of thepiston 5. When the piston 5 rotates in the counterclockwise directionwith respect to the cylinder 4, fluid entering in each recess 334 a,such as lubrication oil, is forced to flow toward the narrowed edgeportion of the triangular recess 334 a in accordance with the rotationof the piston 5, increasing the pressure in proportion to the reductionof the triangular cross section according to the wedge effect. Theeffect of the generated dynamic pressure is remarkable at the portionwhere a clearance between the piston 5 and the cylinder 4 is small.Accordingly, the generated dynamic pressure equalizes the axis of thepiston 5 with the axis of the cylinder 4 and provides a uniformclearance between the piston 5 and the cylinder 4.

Accordingly, it becomes possible to reduce the coolant gas leakingthrough a slide surface between the piston 5 and the cylinder 4. Thecooling power is increased. Furthermore, elimination of the offset orinclination of the axes of the piston 5 and the cylinder 4 effectivelysuppresses the friction at the slide portion between the piston 5 andthe cylinder 4. Thus, the slide loss can be reduced and the compressorefficiency can be improved.

As described above, the fifteenth embodiment of the present inventionprovides the oscillation-type compressor comprising the block 302 andthe piston 5, the motor 3 including the stator 3 a and the mover 3 b,the movable element 12 including the mover 3 b and the piston 5, thestationary element 13 including the block 302 and the stator 3 a, theelastic element 330 having a portion fixed to the movable element 12 andanother portion fixed to the stationary element 13, the rotationaldirection restricting mechanism 337 for limiting the rotation of theelastic element 330 about the shaft of the piston 5 in a singledirection, the cylinder 4 accommodating the piston 5 so as to allow thepiston 5 reciprocating in the axial direction, and the dynamic pressuregenerating mechanism 334 provided on at least one of the piston 5 andthe cylinder 4. With this arrangement, the elastic element causes arotational displacement in response to a deformation of the elasticelement caused by the reciprocative movement of the movable element. Asthe elastic element can rotate in a single direction with respect to thestationary element, the piston always rotates in the same direction. Thedynamic pressure generating mechanism is provided on a sliding surfaceof the piston and the cylinder. The rotation of the piston causes thedynamic pressure generating mechanism to generate a dynamic pressureacting between the piston and the cylinder. The generated dynamicpressure equalizes the axis of the piston with the axis of the cylinderand provides a uniform clearance between the piston and the cylinder.Thus, it becomes possible to prevent the coolant gas leakage from thecompression chamber. Furthermore, elimination of the offset orinclination of the axes of the cylinder and the piston effectivelysuppresses the friction at the slide portion between the piston and thecylinder. Thus, the slide loss can be reduced and the compressorefficiency can be improved.

The above-described fifteenth embodiment discloses the spiral elasticelement. However, similar effects will be obtained even when thiselastic element is replaced by any other elastic element which iscapable of causing a rotational displacement in response to an axialdisplacement.

Sixteenth Embodiment

FIG. 20 is a vertical cross-sectional view showing an oscillation-typecompressor in accordance with a sixteenth embodiment of the presentinvention. FIG. 21 is a view showing an elastic member used in theoscillation-type compressor in accordance with the sixteenth embodimentof the present invention. In FIGS. 20 and 21, the oscillation-typecompressor comprises a tightly closed casing 1 and a main body 2. Themain body 2 comprises a motor 3, a cylinder 4, a piston 5, a block 6, acylinder dead 7, and an elastic element 8. The main body 2 iselastically supported by a suspension spring (not shown) in the tightlyclosed casing 1.

The motor 3 comprises a stator 3 a and a mover 3 b. A permanent magnet 3c is fixed to the stator 3 a. The mover 3 b (coil) is fixedly connectedto the piston 5 via a mover connecting member 409.

The piston 5, the mover 3 b of the motor 3, and the mover connectingmember 409 cooperatively constitute a movable element 12. The cylinder4, the stator 3 a of the motor 3, and the block 6 cooperativelyconstitute a stationary element 13.

The elastic element 8 comprises a plurality of stacked or multilayeredelastic members 8 a. An inner cylindrical portion 8 b of the elasticelement 8 is fixed to the piston 5. An outer cylindrical portion 8 c ofthe elastic element 8 is fixed to the block 6. Each elastic member 8 acomprises a plurality of spiral slits 8 f so as to function as a spring.

The piston 5, supported by the cylinder 4 and the elastic element 8, isslidable in the axial direction. The cylinder 4 and the piston 5cooperatively define a compression chamber 9.

Next, compression mechanism of the above-described oscillation-typecompressor will be explained. When alternating current is supplied tothe mover 3 b (coil) of the motor 3, the permanent magnet 3 c generatesa magnetic field. Interaction of the mover 3 b with this magnetic fieldgenerates a force for reciprocating the mover 3 b in the axialdirection. The piston 5, connected to the mover 3 b via the moverconnecting member 409, deforms the elastic element 8. Utilizing areaction force given from the elastic element 8, the piston 5continuously repeats the axial reciprocative movement.

Furthermore, when the inner cylindrical portion 8 b of the elasticmember 8 a shifts in the up-and-down direction normal to the plane ofFIG. 21, the inner cylindrical portion 8 b of the elastic member 8 arotates in a direction shown by an arrow shown in FIG. 21. Accordingly,the piston 5 fixed to the inner cylindrical portion 8 b of the elasticmember 8 a rotates in response to the displacement of the elasticelement 8 a. The piston 5 rotates in changed directions and continuesreciprocating.

Coolant gas of a cooling system (not shown) is introduced into alow-pressure chamber 7 a of a cylinder head 7 and then enters thecompression chamber 9 of the cylinder 4 via an intake valve (not shown)disposed in the cylinder head 7. The coolant gas introduced in thecompression chamber 9 is compressed by the piston 5 which reciprocatesin the above-described manner. The compressed coolant gas enters ahigh-pressure chamber 7 b of the cylinder head 7 via an exhaust valve(not shown), and then exits the cylinder head 7 to the cooling system.

In FIG. 20, a support mechanism 413 comprises stationary support members414 a and 414 b fixed to the stationary element 13 and movable supportmembers 415 a and 415 b fixed to the movable element 12. The stationarysupport member 414 a is disposed closely to the compression chamber 9than the other stationary support member 414 b. The movable supportmember 415 a is disposed closely to the compression chamber 9 than theother movable support member 415 b. The movable support members 415 aand 415 b are put between the stationary support members 414 a and 414 band axially offset inward than the corresponding stationary supportmembers 414 a and 414 b.

Operation of the oscillation-type compressor of the sixteenth embodimentwill be explained.

During the compressing operation of the compressor, the piston 5reciprocates in the cylinder 4. When the piston 5 shifts closely to thecompression chamber 9 than its stop position, the elastic element 8deforms in response to a shift movement of the piston 5. The elasticelement 8 has a radial rigidity decreasing in accordance with itsdeformation amount.

Similarly, when the piston 5 shifts far from the compression chamber 9than its stop position, the elastic element 8 deforms in response to ashift movement of the piston 5. The rigidity of the elastic element 8decreases in accordance with its deformation amount.

In the motor 3, air gap provided for separating the mover 3 b from thestator 3 a is not completely uniform. Therefore, the mover 3 b is alwaysattracted toward the stator 3 a in a certain radial direction.

When the piston 5 is positioned closely to its stop position, theelastic element 8 causes a smaller deformation. The radial rigidity ofthe elastic element 8 is sufficiently high. In this case, even when themover 3 b of the motor 3 is radially attracted in the radial directiondue to the uneven air gap, support of the movable element 12 in theradial direction can be done with the slide portion between the piston 5and the cylinder 4 and the elastic element 8. No local side pressurewill act on the slide portion between the piston 5 and the cylinder 4.

When the piston 5 is positioned near the top dead center or the bottomdead center, the elastic element 8 deforms largely with decreased radialrigidity. Thus, the elastic element 8 cannot sufficiently support themovable element 12 in the radial direction.

However, when the piston 5 is positioned near the top dead center, thestationary support member 414 a fixed to the stationary element 13engages with the movable support member 415 a fixed to the movableelement 12 so that the stationary support member 414 a substantiallysupports the movable support member 415 a in the radial direction. Whenthe piston 5 is positioned near the bottom dead center, the stationarysupport member 414 b fixed to the stationary element 13 engages with themovable support member 415 b fixed to the movable element 12 so that thestationary support member 414 b substantially supports the movablesupport member 415 b in the radial direction.

Accordingly, it becomes possible to support the movable element 12 inthe radial direction at the support mechanism 413 in addition to theslide portion between the piston 5 and the cylinder 4 and the elasticelement 8, even when the piston 5 is positioned near the top dead centeror the bottom dead center and therefore the elastic element 8 cannotsufficiently support the movable element 12 in the radial direction dueto reduced rigidity. Thus, this embodiment eliminates the local sidepressure acting on the slide portion between the piston 5 and thecylinder 4, while preventing the deterioration of reliability, such asreduction in the compressor efficiency and the wear occurring at theslide portion between the piston 5 and the cylinder 4.

As described above, the sixteenth embodiment of the present inventionprovides the oscillation-type compressor comprising the tightly closedcasing 1, the piston 5 and the cylinder 4 accommodated in the tightlyclosed casing 1, the motor 3 including the stator 3 a and the mover 3 b,the stationary element 13 including the cylinder 4 and the stator 3 a ofthe motor 3, the movable element 12 including the piston 5 and the mover3 b of the motor 3, the elastic element 8 having a portion fixed orconnected to the movable element 12 and another portion fixed orconnected to the stationary element 13, and the support mechanism 413for supporting the movable element 12 in the radial direction when thepiston 5 is positioned near the top dead center position or the bottomdead center. This arrangement makes it possible to support the movableelement 12 in the radial direction at the support mechanism 413 inaddition to the slide portion between the piston 5 and the cylinder 4and the elastic element 8, even when the piston 5 is positioned near thetop dead center or the bottom dead center and therefore the elasticelement 8 cannot sufficiently support the movable element 12 in theradial direction due to reduced rigidity.

Thus, the sixteenth embodiment eliminates the local side pressure actingon the slide portion between the piston 5 and the cylinder 4, whilepreventing the deterioration of reliability, such as reduction in thecompressor efficiency and wear occurring at the slide portion betweenthe piston 5 and the cylinder 4.

Although the above-described sixteenth embodiment discloses the elasticelement 8 including a plurality of multilayered elastic members 8 a eachcomprising a plurality of slits 8 f, the elastic element 8 can beconstituted by any other comparable elastic element capable ofreciprocating the piston 5 and having a radial rigidity reducing inaccordance with its deformation amount.

Although the above-described sixteenth embodiment discloses the motor 3comprising the motor 3 a and the mover 3 b, any other motor arrangementfor reciprocating the piston 5 can be used.

Although the above-described sixteenth embodiment discloses the elasticelement 8 directly fixed to the piston 5, it is possible to use aconnecting member for fixing the elastic element 8 to the piston 5 or itis possible to connect them in the axial direction.

Seventeenth Embodiment

FIG. 22 is an oscillation-type compressor in accordance with aseventeenth embodiment of the present invention.

The seventeenth embodiment differs from the sixteenth embodiment in thatthe movable element 12 is equipped with a position changing mechanism416. The position changing mechanism 416 can change an axial position ofthe movable element 12. For example, the position changing mechanism 416is a shape memory alloy whose axial length is short when the temperatureis low and long when the temperature is high.

Operation of the oscillation-type compressor in accordance with theseventeenth embodiment will be explained.

The compression chamber 9 is held at a lower pressure due toinsufficiently pressurization immediately after the startup of thecompressor or when the ambient air temperature is low. A gas pressureavailable for shifting the piston 5 away from the compression chamber 9is small. Accordingly, the oscillation center of the piston 5 isdislocated so closely to the compression chamber 9 that the piston 5 maycollide with the cylinder head 7 or the exhaust valve.

However, in such operating conditions, the position changing mechanism416 has a short axial length due to the low temperature of thecompression chamber. Accordingly, the top dead center position of thepiston 5 is sufficiently far from the cylinder head 7 and the exhaustvalve so that the piston 5 can be prevented from colliding with thecylinder head 7 and the exhaust valve. This prevents the cylinder head 7and the exhaust valve from being damaged. Noise is generated.

Furthermore, when the compressor temperature reaches a higher level inaccordance with elapse of time, or when the ambient temperature is high,attained pressurization is sufficiently high. In such operatingconditions, a sufficiently large gas pressure is available for shiftingthe piston 5 in the direction opposed to the compression chamber 9.Accordingly, the oscillation center of the piston 5 is dislocated awayfrom the compression chamber 9 so as to separate the piston 5sufficiently far away from the cylinder head 7 and the exhaust valve,causing no collision between them.

On the contrary, the piston 5 may not reach the ordinary top deadcenter. The top clearance of the piston will increase excessively,causing significant reduction in the cooling power and in the compressorefficiency. However, in such operating conditions, the position changingmechanism 416 has a long axial length due to increased compressortemperature. Thus, the position changing mechanism 416 dislocates thetop dead center of the piston 5 toward the cylinder head 7 and theexhaust valve. Thus, it becomes possible to prevent the top clearance ofthe piston 5 from increasing excessively and realize an ordinaryoperation satisfactory in the cooling power as well as the compressionefficiency.

As described above, the seventeenth embodiment of the present inventionprovides the oscillation-type compressor comprising the tightly closedcasing 1, the piston 5 and the cylinder 4 accommodated in the tightlyclosed casing 1, the motor 3 including the stator 3 a and the mover 3 b,the stationary element 13 including the cylinder 4 and the stator 3 a ofthe motor 3, the movable element 12 including the piston 5 and the mover3 b of the motor 3, the elastic element 8 having a portion fixed to themovable element 12 and another portion fixed to the stationary element13, and the position changing mechanism 416 associated with the movableelement 12 for changing an axial position of the movable element 12.With this arrangement, it becomes possible to prevent the piston 5 fromcolliding with the cylinder head 7 or the exhaust valve when the movableelement 12 including the piston 5 is dislocated toward the compressionchamber 9 due to the insufficient pressurization occurring immediatelyafter the startup of the compressor or when the ambient air temperatureis low. Thus, the seventeenth embodiment of the present inventionprevents the compressor from being damaged, while adequately maintainingthe reliability. Noise is suppressed.

Furthermore, when the compressor temperature reaches a higher level inaccordance with elapse of time, or when the ambient temperature is high,the attained pressurization is sufficiently high. In such operatingconditions, the movable element 12 including the piston 5 is dislocatedaway from the compression chamber 9. However, the seventeenth embodimentof the present invention prevents the top clearance of the piston 5 fromincreasing excessively and realizes an ordinary operation satisfactoryin the cooling power as well as the compression efficiency.

The position changing mechanism 416 disclosed in the above-describedseventeenth embodiment is the functional element whose axial length isvariable in response to the temperature change. However, the positionchanging mechanism 416 can be constituted by any other comparableelement capable of changing the axial position of the movable element 12in response to changed external temperature and pressure conditions.

Although the above-described seventeenth embodiment discloses the motor3 comprising the motor 3 a and the mover 3 b, any other motorarrangement for reciprocating the piston 5 can be used.

Eighteenth Embodiment

FIG. 23 is an oscillation-type compressor in accordance with aneighteenth embodiment of the present invention.

The eighteenth embodiment differs from the seventeenth embodiment inthat a stopper 417 is provided to limit an axial shift amount of themovable element 12 changed by the position changing mechanism 416.

Operation of the oscillation-type compressor in accordance with theeighteenth embodiment will be explained.

The compression chamber 9 is held at a lower pressure due toinsufficiently pressurization immediately after the startup of thecompressor or when the ambient air temperature is low. A gas pressureavailable for shifting the piston 5 away from the compression chamber 9is small. Accordingly, the oscillation center of the piston 5 isdislocated toward the compression chamber 9. The piston 5 may collidewith the cylinder head 7 or the exhaust valve.

However, in such operating conditions, the position changing mechanism416 has a short axial length due to the low temperature of thecompression chamber. Accordingly, the top dead center position of thepiston 5 is sufficiently far from the cylinder head 7 and the exhaustvalve so that the piston 5 can be prevented from colliding with thecylinder head 7 and the exhaust valve. This prevents the cylinder head 7and the exhaust valve from being damaged. Noise is generated.

The axial length of the position changing mechanism 416 may be extremelydecreased in response to extremely changed operating conditionsincluding the sudden changes in the ambient air temperature or in thepressurization. However, when the axial length of the position changingmechanism 416 becomes shorter than a predetermined value, an end surface417 a of the stopper 417 is brought into contact with the elasticelement 8. Thus, the stopper 417 restricts the excessive shift movementof the movable element 12 away from the compression chamber 9.

Accordingly, it becomes possible to prevent the top clearance of thepiston from increasing excessively and to realize an ordinary operationsatisfactory in the cooling power as well as the compression efficiency.

As described above, the eighteenth embodiment of the present inventionprovides the oscillation-type compressor further comprising the stopper417 for limiting the axial shift amount of the movable element 12changed by the position changing mechanism 416. With this arrangement,it becomes possible to prevent the movable element 12 from excessivelyshifting away from the compression chamber 9 in response to extremelychanged operating conditions including the sudden changes in the ambientair temperature or in the pressurization, thereby eliminatingdeterioration of the cooling power and lack of the compression.

This invention may be embodied in several forms without departing fromthe spirit of essential characteristics thereof. The present embodimentsas described are therefore intended to be only illustrative and notrestrictive, since the scope of the. invention is defined by theappended claims rather than by the description preceding them. Allchanges that fall within the metes and bounds of the claims, orequivalents of such metes and bounds, are therefore intended to beembraced by the claims.

What is claimed is:
 1. An oscillation-type compressor comprising: atightly closed casing having an inside space for storing coolant gas; acylinder accommodated in said tightly closed casing; a motor including astator and a mover; a piston connected to said mover of said motor; amovable element including said mover of said motor and said piston; astationary element including said stator of said motor and saidcylinder; an elastic element having a portion fixed to said movableelement and another portion fixed to said stationary element; a pistonposition detecting sensor detecting the position of said piston; topdead center position calculating means for calculating a top dead centerposition of said piston based on a piston position signal obtained fromsaid piston position detecting sensor; amplitude control means forcontrolling an amplitude of said mover in accordance with a differencebetween said top dead center position and a selected top dead centerreference value; and top dead center reference value changing means forchanging said top dead center reference value.